Grain boundary effects on spinodal decomposition: II. Discontinuous microstructures Original Research Article

We have used a phase field model of a polycrystalline alloy, presented in [Acta Mater. 51 (2003) 4761], to study the effect of enhanced atomic mobility at the grain boundary (GB) on spinodal decomposition (SD) in two dimensional systems. For sufficiently large values of atomic mobility at the GB (Mg), and of GB mobility (Lg), fast decomposition along the boundary converts it into a transformation front, whose migration leaves behind a discontinuous microstructure consisting of alternating A-rich and B-rich lamellae. We present a theory of discontinuous SD under the assumption of a small degree of decomposition in the lamellae (i.e., large values of Lg/Mg). In this limit, for a given Mg, increasing Lg leads to a decrease in the degree of decomposition in the lamellae, but does not alter the lamellar spacing and front velocity, which remain constant. The results from our simulations are in good agreement with these theoretical predictions.